Patents which are pertinent to the subject matter of this invention are as follows: U.S. Pat. Nos. 3,883,218, (May 13, 1975); 3,984,172 (Oct. 5, 1975); 3,920,432 (Nov. 18, 1975); 3,937,559 (Feb. 10, 1976).
A property of glass optical fibers that makes cabling them difficult is that glass fibers are very small and their axes can be easily distorted sharply, by asymmetric forces of very small magnitude which in turn causes increase in attenuation. Almost all surfaces of cable components, including plastic buffering on fibers, are imperfect; therefore, in the presence of necessary forces required for cabling in long lengths, control of attenuation of the fibers become extremely difficult in conventional cabling.
The primary advantage a sub-assembly can provide is that the multiple-fiber composite becomes stronger and can be considerably more rigid reducing the proneness to microdistortion of fiber axes and, therefore, improved control over fiber performance in the cable. The principal features required for such a sub-assembly are minimal increase in attenuation in forming the sub-assembly, and reduced proneness to microdistortion of fiber axes in the sub-assembly.
Other features that become important in such sub-assemblies, due to practical considerations, are mechanically strippability for ease of cable termination and splicing; small size; and ease of identification through color code.
The improved package provided by the present invention includes a laminate in which the optical fibers are held between two films with the optical fibers secured to one of the films by pressure sensitive adhesive which permits the fibers to be connected with the film without the use of adhesive which might affect the length, width and/or flatness of the films. The optical fibers are covered by a second film, with the second film preferably thinner than the first film and connected to the first film along the edges of the film. The invention provides spacers to eliminate assymetric pressure of the second film on the edge fibers as secured to the first film.
An integral feature of the construction is that it is assymetric in nature, that is, the fiber axes are away from the neutral axis of the assembly so that each fiber in the assembly is in minimum tension when cabled. One advantage derived from this is that it is possible to provide extra stiffness, for instance, without delamination forces being too high, in the assembly for reduced microbending during cabling.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.